Generally, casting is the process by which molten material is formed into solid shapes. A known method for casting materials has involved the use of rolling cylinders to compress slabs of cast material to a desired thickness. However, this process is very energy intensive and costly.
An alternative casting method for producing a strip of material of a desired thickness, known as strip casting, incorporates a rotating wheel, drum, belt or other substrate. The rotating substrate is placed in close proximity to a casting nozzle from which molten material flows. The molten material is deposited on the rotating substrate where it cools, solidifies or "freezes", and is subsequently removed for further processing.
However, when the molten material is initially introduced through the casting nozzle and onto the casting wheel, heat is exchanged from the high temperature molten material to the lower temperature casting nozzle and casting wheel. This transfer of heat energy to the casting nozzle and the casting wheel causes them to expand, often in an unpredictable and non-uniform manner. As a result of this expansion, the distance between the adjacent surfaces of the casting wheel and the casting nozzle is often reduced.
Until the temperatures of the casting nozzle and the casting wheel reach a steady state, at which time further expansion of the casting nozzle and the casting wheel is minimized, the gap between them will not be a uniform or constant distance. In at least the case of planar flow casting, an example of which is illustrated in U.S. Pat. No. 4,771,820, the gap between the casting nozzle and the casting substrate can affect the thickness of the cast material, which is generally crucial to the quality of the cast material. If the cast material does not have the desired thickness, it may either be scrapped or mechanically reformed, both of which are expensive, time consuming, and inefficient.
The inability to control and maintain a desired distance or gap between the casting nozzle and the casting wheel can also cause a variety of other problems during casting. For example, if the distance between the casting nozzle and the casting wheel becomes too large, the molten material can flow along the face of the casting nozzle rather than onto the casting wheel. Material which is not deposited onto the casting wheel will inherently begin to cool as it flows along the nozzle, and can thereby interfere with the efficient operation of the machinery and compromise the quality and uniformity of the resultant cast product. Conversely, if a minimum gap between the casting nozzle and the casting wheel is not maintained, contact may occur between them which can result in severe damage to both the nozzle and the wheel. Such a situation obviously interferes with the safety and efficiency of the casting process.
In particular, when steel and other high temperature materials are strip cast, the relative expansions of the casting nozzle and casting wheel are virtually impossible to avoid. Since it is not generally economical to pre-heat a casting nozzle and a casting wheel to their steady state temperatures, a variety of methods have been used to measure and maintain the distance between a casting nozzle and a casting wheel. An example of an unique electronic device and method for monitoring and maintaining this distance involving the flow of electricity between the casting nozzle and the surface of the casting wheel is disclosed in the commonly owned U.S. Patent Application entitled ELECTRONIC GAP SENSOR AND METHOD, filed concurrently herewith in the names of Robert S Williams, Edward L. King, and Steven L. Campbell.
A known method of measuring the distance between a casting nozzle and a casting wheel using lasers is disclosed in U.S. Pat. No. 4,399,861, which issued to Carlson on Aug. 23, 1983. In the Carlson patent, a laser beam is transversely projected along the gap between a casting nozzle and a casting wheel. Photodiodes are provided to detect the presence of the laser beam on the other side of the gap, from which, as described in the Carlson patent, the gap can then be calculated.
However, the use of lasers has several drawbacks. In particular, laser methods and equipment are generally expensive and complicated to perform, especially for casts of wide strips of very hot alloys such as steel. In addition, lasers require a straight line of sight between the laser source and the laser detector, through which the laser beam may travel. Providing that unencumbered passageway is often impractical between the expanding casting nozzle and substrate. Moreover, the presence of smoke, heat, dust and other gases and particles produced during casting may interfere with and restrict the passage of a laser beam through the gap.
An example of a device using a pressure sensor to measure imperfections on a machined roll is disclosed in U.S. Pat. No. 4,524,546, which issued to Hoover et al., on June 25, 1985. The Hoover patent discloses a sensor which uses a pressurized fluid such as air to measure the distance between the sensor and a machined roll. The air is provided by a regulator to the sensor and is expelled through an outlet orifice in proximity with the roll. When the air leaves the outlet orifice, it encounters a resistance from the adjacent surface of the roll, restricting the flow of air out of the sensor. This resistance results in an increased pressure in the sensor which can be detected by a pressure transducer. Differences in pressure signify different distances between the sensor and the roll. The recording of these differences on a chart recorder allows for the measurement of the crown and taper in a roll without removing the roll from the grinding station.
However, the pressure sensor disclosed in the Hoover patent is not used as a means for determining the gap between a casting nozzle and a moving substrate. Furthermore, the device disclosed in the Hoover patent is not designed to function in the high temperatures and hostile environment associated with casting. Moreover, the Hoover sensor is not used as a means for selectively adjusting the relative positions of a casting nozzle and a casting substrate.
Consequently, heretofore, there has not been available a suitable low cost and reliable means for measuring and maintaining a predetermined gap between a casting nozzle and a casting wheel which does not physically contact the casting wheel. Furthermore, there has not been available a dependable sensing device for pneumatically measuring the gap within the unique and hostile environment between a casting nozzle and a casting wheel. Additionally, there is a need in the industry, which heretofore has not been fulfilled, for accurately, reliably, and relatively inexpensively regulating the position of a casting nozzle with respect to a casting wheel along one or more axes.